Direction finding antenna system



Nov. 30, 1948. e. s. BuRRouGl-ls nnmc'rron FINDvING ANTENNA SYSTEM Filed.nine 25, 1945 .www

, QNUSWR maks atented 2,454,768 DIRECTION FINDING ANTENNA SYSTEM GordonS. Burroughs. Forest Hills, N. Y., assignor to Federal Telephone andRadio Corporation,

` `New York, N. Y., a corporation oi Delaware Application June Z5, 1945,Serial No. 601,386

The present invention relates to direction ilnders and particularly tothat type of direction nder which utilizes an elevated H" Adcock typeantenna system.

Ii a perfectly symmetrical antenna system of the H Adcock type werelocated in free space remote from all objects, no polarization errorswould be introduced. In attempting to approximate this condition, sucharrays have been arranged on wooden towers high above the ground. Whilethis has to some extent lessened the effect of proximity to ground, it`has not altogether obviated it. Furthermore the use of very high towersis, in many cases, impractical particularly. for portable directionfinders. When waves having horizontal components impinge on thehorizontal conductive membersfthey induce'voltages in said members.These members are capacitively coupled through many .stray capacitancesto the antenna units and introduce voltages into said antenna units. Ifthe introduced voltages balance, there will be no resultant output dueto the horizontal wave components. straycapacitances are not symmetricalin the antenna system due to the proximity to earth and other bodies, aswell as other factors, `these introduced voltages tend to be unequal andto introduce error. The problemv is further aggravated by-localconditions which are changing and require rebalancing of the system, andeven more so when the system is moved from place to place as in portableunits.

Since these 14 claims. (ci. 34a-11s) Y 2 so asto substantially eliminatepolarization errors.

Another object of the present invention is the provision of apparatusand a method associated with a direction finder whereby such antennasystems may be readily balanced or rebalanced by relatively un killedpersonnel.

Still another object of the present invention is the provision ofapparatus and a method for adjusting such antenna system to obtain agood null.

A further object of the present invention is the vprovision of adirection finder including an antenna system of the type referred tohereinabove including apparatus enabling the ready adjustmy invention.

Referring now to the ligure, the H" type Adcock antena system thereillustrated, includes four antenna units I-t of which antenna units Iand 2 are the upper pair and 3 and I are the lower pair, with antennaunits I and 3 being on the left side and antenna units 2 and t being onthe right side as viewed in said gure. Antenna In such systems anotherproblem, which comincluding its leads is electrically substantially.

symmetrical.

An object of the present invention is the provision of apparatus and amethod for adjusting an antenna system of the type described so as toproduce substantially electrical symmetry therein.

Another object of the present invention is ,the provision of anapparatus and method for balancing an antenna system of the typereferred to units I-- are cross-connected by transmission lines 5 and 6.However, in accordance with my invention, transmission lines 5 and 6,which may be in the form of coaxial lines, are not directly connected tosaid antennas but are coupled to said antenna units through couplers forantenna units I-t respectively.

In accordance with my invention, balancing is accomplished bycontrolling the relative gain of the coupling units 'l-I I prefer toemploy coupiers which, while giving variable gain, are relativelyconstant in regard to their impedance as seen from the output line andwhich are also free of changes of phase. For this purpose I prefer touse anode-loaded circuitsas the couplers. A typical example of such ananode-loaded circuit is illustrated schematically in coupling unit 8, it

being understood that the other coupling units are similar inconstruction. In coupling unit il, it will be seen that antenna unit 2is connected to the 'gridI II of an electron discharge device I2 whoseanode I3 is connected through a suitable load resistor It to a source of B power supply I5.

aecaree it being' understood that the negative side of said source isconnected to ground. The radio frequency output of the coupling unit istaken from anode I3 to a coupling condenser I3 which is; in turn,connected to one end of transmission line i5. The other end of saidtransmission line 6 being connected to the radio frequency output ofcoupling unit 9. Similarly the radio frequency output of coupling unit 1is connected with the radio frequency output of coupling unit I by line3. The cathode I1 is connected through a by-pass condenser I9 to ground(the chassis of the coupling unit). Bias for the cathode is suppliedthrough a cathode resistor which is likewise used to control the gain.For this purpose the cathode I1y is connected by a lead I9 toutheinterior of the direction iinding receiver 20. Similar leads 2l, 22 and23 connect the cathodes o coupling units 1, 9 and I0 respectively to theinterior of the direction finding receiver.

As pointed out hereinbeiore, the antenna system symmetry is obtained bybalancing the gain from the coupling units 1-I0, which in turn, iscontrolled by controlling the D. C. Abias applied to the cathode bycontrolling the relative value of the cathode resistors. Furthermore.the foregoing adjustments are made so simply that an unskilled personcould readily make them. For this purpose the following arrangement isemployed. Leads I9 and 2l are connected to the opposite ends of theresistor oi a potentiometer 24 while leads 22 and 23 are connected tothe opposite ends of the resistor of a potentiometer 25.

A third potentiometer 26 is employed whose movable arm is connected toground. The potentiometers 24, 23 and 23 are interconnected by means ofa multiple contact rotary switch 21 consisting of two sections 2t and 29each having three contacts 39-32 and 33-35 respectively and havingswitch arms 36 and 31 respectively, said switch arms 35 and 31 beingganged together. The movable arm of potentiometer 24 is connected tocontacts 30 and 32 with contact 3i being a blank. The movable arm ofpotentiometer 25 is connected to the switch arm 31. Contact 33 is ablank while contacts 34 and 35 are connected together and to one end ofthe resistor yof potentiometer 23. The other end of said resistor beingconnected to the switch arm 33. The other connections of the directionfinder may be conventional, that is, the transmission lines and 6 whichinterconnect the antenna units, in turn, are coupled to the directioniinding receiver at their midpoints over transmission lines 38 and 39. Asensing antenna llil with a coupler 4I and a transmission line 42 iscoupled into the direction finding receiver and the direction findingreceiver has at its output an indicator 43, which may be in the form ofa vacuum tube voltmeter arrangement such as is described in my copendingapplication, G. S. Burroughs, for Comparison system, Serial No. 592,401,iiled May '1, 1945, now abandoned, or any other suitable indicatingdevice.

In adjusting the antenna system in accordance with my invention, atarget transmitter 44 is employed which is optically sighted so that thedirection of the wave transmitted from said transmitter will betransverse and perpendicular to the common plane of the antenna units.In the iirst operation, the antenna system is balanced as to receptionfrom the two upper antenna units I and 2. In the second step the twolower antenna units 3 and 4 are balanced. In. the

third step the upper units are balanced against the lower units. In thefirst two steps, the balance is made as to vertcially polarized wavesand in the third step the balance is made as to a horizontally polarizedwave, the target transmitter 44 being turned around for this last stepto transmit horizontally polarized waves.

For the first step the knob of the switch 21 is turned into a iirstposition in which switch arm 33 is on contact 30 and switch arm 31 is oncontact 83. It will be seen that in this position the couplers t and I9will be inoperative due to the fact that the cathode circuit is notcompleted to ground and so energy from antenna units 3 and 4 will not bedelivered to the receiver while at the same time it will be seen thatthe couplers 1 and 8 associated with antenna units I and 2 respectivelywill be connected to ground through potentiometer 24 and potentiometer23, and since, as stated before, the negative side of the B" supply isconnected to ground, a bias is provided on the cathode of coupling unitsl1 and 3. The relative bias on these two coupling units is then adjustedby adjusting the position of the potentiometer arm of potentiometer 24.This adjustment is made while observing the indicator 43 until a zeroreading is obtained on said indicator, that is, a reading which willindicate that the input derived from antennas I and 2 is exactly equal.

For the second step the switch 21 is moved into the second position witharm 33 on contact 3l and arm 31 on contact 34. In this position cou-'pling units I and 8 are inoperative and therefore antenna units I and 2are disconnected from the receiver whereas antenna units 3 and 4 arecoupled to the receiver. By adjusting the potentiometer arm oipotentiometer until the indicator 43 indicates a zero reading, theoutputs derived from said antenna units 3 and 4 are then balanced.

The first two steps serve to balance the antenna system in regard tovertical polarization so that the antenna system is effectivelysymmetrical in regard to such polarization and the system is so balancedthat when it is transverse and perpendicular to the direction from whichenergy is being transmitted, no output will be produced thus providing asharp null.

The purpose of the third step is to eliminate the difference between thecurrents induced by horizontal polarization in the upper and lowerportions of the antenna system and thus minimize the polarization error.For the third step the transmitter 44 is caused to transmit horizontallypolarized waves. Switch 21 is then moved to its third position withswitch arm 38 on contact 32 and switch 31 on contact 35. It

will be seen that in this position all ofthe coupling units 1-i0 areoperative and therefore their respective antennas are coupled to thedirection iinding receiver. In this position the movable arm ofpotentiometer 23 is moved so as to produce a zero indication in theindicator 43. This balances the horizontal pick-up of theA upper portionof the antenna system against the horizontalpolarizatlon pick-up of thelower portion of said antenna system. After this third step has beencompleted, the antenna system is substantially electrically symmetricala'nd is balanced in regard to horizontal polarization.

While I have described the details of one method and associatedapparatus for balancing an antenna system of this type. it will beapparent to those versed in the art from my teachings departing! fromthe teachings of my invention.

For example, other types of circuits, including other anode-loadedcircuits than that illustrated here may be employed. Furthermore theswitch 21 may be provided with other sections and other contact arms, aswell as with additional potentiometers and other adjusting means, toproduce .various other adjusting operations in connection with thedirection iinding receiver. The same sequence of operations, that is,the movement of the switch 21 from one position to a next and then theadjustment oi the associated control may be carried out in more complexform in regard to further adjustment of the receiver "such as balancingof ampliiiers therein as, for example, in my copending application C. S.Burroughs, for Comparison system," Serial No. 592,401, filed May 7,1945, and various other adjustments known to those versed in the art.Accordingly, while I have described above the principles o1' myinvention in connection with specific apparatus, it is to be clearlyunderstood that this description is made only by way of example and notas a limitation on the scope oi' my invention as defined in theaccompanying claims.

I claim: A,

1. In combination, an antenna system having a plurality of upper andlower radiantacting elements mounted in the same plane, each of saidelements having separate output circuits, and

means controlling the gain oi' said upper element circuits and separatemeans for independently controlling the gain of said lower elementcircuits for balancing said outputs.

'2. An arrangement as set forth in claim 1, wherein said circuits eachcomprise an electron discharge device having an anode load for providingconstant impedance as seen from said outputs, and means controlling therelative gain of said devices balancing said outputs.

3. An antenna system comprisinga plurality of upper and lower antennaunits, mounted in the same plane a plurality of circuits each having itsoutput coupled toa separate one of said units,

and means controlling the relative gain of saidupper unit circuits andsaid lower unit circuits to balance the resultant output.

4. An antenna system comprising a plurality of upper and lower antennaunits mounted in the same plane and providing a radiant action patternhaving a null direction, a plurality of circuits each having its inputcoupled to a separate one of said units, and means controlling therelative gain of said upper and lower unit circuits to produce equaloutputs from said upper and lower units with respect to electromagneticwaves received from the null direction.

5. In an antenna system comprising a plurality of vertical upper andlower antenna units mounted in the same plane and interconnected byhorizontal lines and providing aradiant action pattern having a nulldirection for vertically polarized waves, a plurality of circuits eachhaving its input coupled to a separate one of-said units and its outputconnected to one end of said lines, and means controlling the gain ofsaid upper unit circuits and means separately controlling the gain ofsaid lower unit circuits to produce equal 'outputs from said upper andsaid lower units respectively ywith respect to vertically polarizedwaves from thenull direction and means for controlling rthe relativegain of said upper unit circuits and said lower unit circuits to produceequal outputs from said upper d and said lower unit circuits withrespect to horl zontally polarized waves from the null direction.

6. An H Adcock antenna system providing a directional pattern having anull direction, comprising a plurality oi antenna units including twospaced vertical upper units and two correspondingly spaced verticallower units with each of the lower units substantially aligned with aseparate one oi the upper units, a plurality of adjustable gain circuitseach having its input connected to a separate one oi said units, andeach positioned adjacent its lassociated unit, a pair of substantiallyhorizontal transmission lines interconnecting the outputs of saidcircuits, the output o! said antenna system being taken across themidpoints oi said horizontal transmission lines, means controlling therelative gain of the upper circuits to balance the outputs derived fromthe upper pair of units with respect to vertically polarized waves fromthe null direction, means lcontrolling the relative gain oi the lowercircuits to balance theA outputs derived from the lower pair of unitswith respect to vertically polarized waves from the null direction, andmeans controlling the gain of the upper circuits in relation to the gainof the lower circuits to balance the outputs derived from the upper pairof units with respect to that from the lower pair of units with respectto horizontally polarized waves from said null direction.

7.. In a direction finding receiver, an "HI Adcock antenna systemproviding a directionallpattern having a null direction comprising aplurality of antenna units including two spaced vertical upper unlts andtwo correspondingly spaced lower units, each of the lower. units beingvertically aligned with a. separate one of the upper units a pluralityof adjustable gain circuits each having its input connected to aseparate one of said units, a pair of horizontal transmission linesinterconnecting the outputs of said circuits, a direction `findingreceiver, means coupling the midpoints of said linesv to said receiver,means con trolling the gain of the upper circuits with relation to thelower circuits to balance the outputs derived from the upper pairs ofunits relative to the lower pairs of units with respect to horizontallypolarized waves in the null direction, means controlling the relativegain of the upper circuits to-balance the outputs derived from the upperpairs of units with respect to vertically polarized waves in the nulldirection, and means controlling the relative gain of the lower pairs ofcircuits to balance the outputs derived from the lower pair of unitswith respect to vertically polarized waves in the null direction.

8. An antenna system according to claim 6 wherein said circuits eachcomprise an electron discharge device.

' 9. A direction finding receiver according to` claim 7 wherein saidvariable gain circuits each comprise an electron discharge device.

10. The method of balancingv an antenna system of the type -providing aradiant action pattern with a directional null and having a pluralityaanwas 7 tem oi' the type providing a radiant action pattern with adirectional null and having a plurality of vertical upper and lowerantenna units mounted in the same plane and each coupled to a separateadjustable gain coupler comprising arranging the antenna system in thenull position with respect to a source of radiant energy transmittingvertically polarized waves and adjusting the gain of said upper unitcouplers and separately adjusting the gain of said lower unit cou-Apiers until the upper unit and the lower unit coupler outputs areequal.

12. The method of balancing an antenna system of the' type providing aradiant action pattern with a directional null and having a pair ofspaced vertical upper and lower antenna units mounted in the same planeand each coupled to a separate adjustable gain coupler comprisingarranging the antenna system in the null position with respect to asource oi radiant energy transmitting vertically polarized waves andadjusting the gain of the upper unit couplers and separately adjustingthe gain of the lower unit couplers until the upper unit and the lowerunit outputs derived from said couplers are equal respectively.

13. The method of balancing an antenna system of the type providing aradiant action pattern with a directional null and having a plurality ofvertical upper and lower antenna units mounted in the same plane andinterconnected by a pair of substantially horizontal transmission linescomprising arranging the antenna system in the null position withrespect to a source of radiant energy transmitting horizontallypolarized waves and adjusting the relative gain of said upper unitcouplers Vand said lower unit couplers until the outputs of said upperunit and said lower `unit couplers are equal.

14. The method of balancing an H" Adcock antenna system providing adirectional pattern having a null direction and including two spacedvertical upper units and two correspondingly spaced vertical lowerunits, a plurality of variable gain couplers each having its inputconnected to a separate one of said units and positioned adjacent itsassociated unit and a pair of substantially horizontal transmissionlines interconnecting the outputs of said circuits comprising arrangingthe antenna system in the null position with respect to a source ofradiant' energy transmitting vertically polarized waves, adjusting thegain of the upper couplers until the output derived from the upperantenna units is equal, adjusting the relative gain of the lowercouplers until the outputs derived from the lower antenna units areequal, causing the target transmitter to transmit horizontally polarizedwaves and in the same null position varying the gain of the uppercouplers with relation to the gain of the lower couplers until theoutputs are equal.

GORDON S. BURROUGHS.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS

